JP 2000-289376 A discloses a plastic-made binder which is used to bind loose-leaf papers on the market or documents punched by a multi-hole puncher. This binder is a one-piece molded product in which a large number of ½ ring portions are arranged at given intervals in two lines on both sides of a back part of the binder, and the back part of the binder itself is a hinge composed of two divided sections. With the back part between the two lines, one line of ½ ring portions respectively include spherical-shaped projections on the leading ends thereof; whereas the other line of ½ ring portions respectively include in the leading ends thereof holes respectively having shapes corresponding to their associated projections. When the spherical-shaped projections and holes are fitted with each other, the two lines of paired ½ ring portions are connected together, thereby binding the loose-leaf papers.
In the field of office automation equipment, there is known a kind of composite machine which includes a copying machine and a stapler incorporated in the copying machine and is capable of carrying out operations ranging from a copying operation to a binding operation. It may be more convenient to be able to provide an automatic binding processing machine which punches holes in copied papers and attaches a binder to the copied papers. It can be estimated that potential demand for such automatic binding processing machine must be large.
To realize this type of binding processing machine, means for handling a binder is an important element. For example, it is necessary for the binder to have a structure suitable for mechanically handling or carrying out binder operations such as binder feeding, holding and fitting operations. However, the binder disclosed in JP 2000-289376 A is structured on the assumption that it is mounted by hand into a binding processing machine but not on the assumption that it is handled mechanically. Thus, it is difficult to use this binder in a binding processing machine which does not require the manual operation.
In view of this, there has been proposed a binder having a structure which is suitable for use in the binding processing machine. For example, a binder disclosed in JP 2004-237578 A is structured such that, the back part of the binder is projected forwardly or toward the back surface of the binder and thus, when a number of binders are piled up on top of each other, the back part of one binder can be contacted with the front surface or back surface of the other binder. According to this structure, even when a large number of binders are piled up on top of each other, the individual binders can be piled up in such a manner they respectively can keep their initial shapes, whereby, when the binders are loaded into a cartridge provided in the binding processing machine, the smoothness of the feeding and mounting of the binders can be improved.
Also, a binder disclosed in JP 2004-237579 A is structured such that one or more recessed portions are formed on one of the front and back surfaces of the back part of the binder, and such that one or more projecting portions to be fitted and paired with the recessed portions are formed on the other surface, whereby a plurality of binders can be connected together while they are piled up on top of each other. This structure can facilitate the handling of the piled-up binders.
Further, a plastic-made binder disclosed in JP 2004-237580 A has a scarf joint structure in which, in the end portions of sectioned ring portions to be fitted and paired with each other, there are provided symmetrical steps extending in the radial direction thereof. Further, this binder includes a hook portion on one end thereof, and a catch portion to be fitted and paired with the hook portion on the other end thereof, thereby providing means for fitting its sectioned ring portions with each other. Therefore, this binder requires less power for fitting when compared with the structure of the binder disclosed in JP 2000-289376 A in which the spherical projections are fitted into the holes. Also, according to this binder, the structure of a die for molding it can be further simplified.
Generally, the coefficient of linear expansion of plastic with respect to temperature is larger than that of metal. Moreover, a product having a large length such as a plastic-made binder varies greatly in length according to temperature. In a binder of a type that is mounted by hand, heat influences can be substantially neglected. However, in a binder which is used in a binding processing machine, since the binder is loaded into the binding processing machine, it can be influenced greatly by the heat of the binding processing machine, thereby raising a possibility that there can be generated a difference between the pitch of holes punched in the papers and the ring pitch of the binder. In this case, when the punched hole in one end of the papers and binder ring, or the punched hole in the central portion of the papers and binder ring are used as standards for positioning, the punched hole in the other end of the papers or the punched holes in the two ends thereof are shifted in position from the binder rings, which may obstruct the fitting or engaging of the binder rings.
Also, in a binding processing machine, when a binder is fed along a binder guide corresponding in shape to the shape of the front surface of the binder, if the binder expands linearly, the side surface of the ring portion is strongly contacted with the wall surface of the binder guide so that feed resistance is increased, which may result in the poor feeding of the binder.